The invention concerns an improved self-retaining roof bolt.
Roof bolts are used in underground mining operations to help support tunnel roofs. Present practice is to drill an approximately 1-inch diameter hole 4 to 6 feet into the tunnel roof. Holes are usually drilled about every 2 feet. The hole is first filled by inserting a rod into the hole and then the face is sealed with a plate. The space between the rod and the wall of the hole is then filled with a cement or resin securing the rod and plate.
The need to support the bolt in the hole until the rod is secured by the cement or resin significantly slows the installation of new bolts and increases the cost of each bolt. For instance, the total in-place cost in a typical mining operation has been estimated at about $12 per bolt, approximately 25% of the total mining cost. Accordingly, a system which might reduce the cost of in-place roof bolts would provide significant savings. One means of reducing the cost of installing roof bolts would be to provide a bolt which does not require external support during the cementing process.